Purine nucleotides and AMP deamination during maximal and endurance swimming exercise in heart and skeletal muscle of rats

Differences in Physiological Responses to Interval Training in Cyclists With and Without Interval Training Experience

The aim of this study was to determine differences in glycolytic metabolite concentrations and work output in response to an all-out interval training session in 23 cyclists with at least 2 years of interval training experience (E) and those inexperienced (IE) in this form of training. The intervention involved subsequent sets of maximal intensity exercise on a cycle ergometer. Each set comprised four 30 s repetitions interspersed with 90 s recovery periods; sets were repeated when blood pH returned to 7.3. Measurements of post-exercise hydrogen (H+) and lactate ion (LA-) concentrations and work output were taken. The experienced cyclists performed significantly more sets of maximal efforts than the inexperienced athletes (5.8 ± 1.2 vs. 4.3 ± 0.9 sets, respectively). Work output decreased in each subsequent set in the IE group and only in the last set in the E group. Distribution of power output changed only in the E group; power decreased in the initial repetitions of set only to increase in the final repetitions. H+ concentration decreased in the third, penultimate, and last sets in the E group and in each subsequent set in the IE group. LA- decreased in the last set in both groups. In conclusion, the experienced cyclists were able to repeatedly induce elevated levels of lactic acidosis. Power output distribution changed with decreased acid–base imbalance. In this way, this group could compensate for a decreased anaerobic metabolism. The above factors allowed cyclists experienced in interval training to perform more sets of maximal exercise without a decrease in power output compared with inexperienced cyclists.

Skeletal muscle mitochondrial DNA content in exercising humans

Several weeks of intense endurance training enhances mitochondrial biogenesis in humans. Whether a single bout of exercise alters skeletal muscle mitochondrial DNA (mtDNA) content remains unexplored. Double-stranded mtDNA, estimated by slot-blot hybridization and real time PCR and expressed as mtDNA-to-nuclear DNA ratio (mtDNA/nDNA) was obtained from the vastus lateralis muscle of healthy human subjects to investigate whether skeletal muscle mtDNA changes during fatiguing and nonfatiguing prolonged moderate intensity [2.0–2.5 h; ∼60% maximal oxygen consumption (V̇o2 max)] and short repeated high-intensity exercise (5–8 min; ∼110% V̇o2 max). In control resting and light exercise (2 h; ∼25% V̇o2 max) studies, mtDNA/nDNA did not change. Conversely, mtDNA/nDNA declined after prolonged fatiguing exercise (0.863 ± 0.061 vs. 1.101 ± 0.067 at baseline; n = 14; P = 0.005), remained lower after 24 h of recovery, and was restored after 1 wk. After nonfatiguing prolonged exercise, mtDNA/nDNA tended to decline ( n = 10; P = 0.083) but was reduced after three repeated high-intensity exercise bouts (0.900 ± 0.049 vs. 1.067 ± 0.071 at baseline; n = 7; P = 0.013). Our findings indicate that prolonged and short repeated intense exercise can lead to significant reductions in human skeletal muscle mtDNA content, which might function as a signal stimulating mitochondrial biogenesis with exercise training.

Possible role of ROS as mediators of hypoxia-induced ion transport inhibition of alveolar epithelial cells

In oxygen-sensitive excitable cells, responses to hypoxia are initiated by membrane depolarization due to closing of the K channels that is thought to be mediated by a decrease in reactive oxygen species (ROS). Because the mechanisms of hypoxic inhibition of ion transport of alveolar epithelial cells (Planes C, Friedlander G, Loiseau A, Amiel C, and Clerici C. Am J Physiol Lung Cell Mol Physiol 271: L70-L78, 1996; Mairbäurl H, Wodopia R, Eckes S, Schulz S, and Bärtsch P. Am J Physiol Lung Cell Mol Physiol 273: L797-L806, 1997) are not yet understood, we tested the possible involvement of a hypoxia-induced change in ROS that might control transport activity. Transport was measured as (86)Rb and (22)Na uptake in A549 cells exposed to normoxia, hyperoxia, or hypoxia together with ROS donors and scavengers. H(2)O(2) < 1 mM did not affect transport, whereas 1 mM H(2)O(2) activated (22)Na uptake (+200%) but inhibited (86)Rb uptake (-30%). Also hyperoxia, aminotriazole plus menadione, and diethyldithiocarbamate inhibited (86)Rb uptake. N-acetyl-L-cysteine, diphenyleneiodonium, and tetramethylpiperidine-N-oxyl, used to reduce ROS, inhibited (86)Rb uptake, thus mimicking the hypoxic effects, whereas deferoxamine, superoxide dismutase, and catalase were ineffective. Also, hypoxic effects on ion transport were not prevented in the presence of H(2)O(2), diethyldithiocarbamate, and N-acetyl-L-cysteine. These results indicate that ion transport of A549 cells is significantly affected by decreasing or increasing cellular ROS levels and that it is possible that certain species of ROS might mediate the hypoxic effects on ion transport of alveolar epithelial cells.

Impairment of cation transport in A549 cells and rat alveolar epithelial cells by hypoxia

A reduced cation reabsorption across the alveolar epithelium decreases water reabsorption from the alveoli and could diminish clearing accumulated fluid. To test whether hypoxia restricts cation transport in alveolar epithelial cells, cation uptake was measured in rat lung alveolar type II pneumocytes (AII cells) in primary culture and in A549 cells exposed to normoxia and hypoxia. In AII and A549 cells, hypoxia caused a PO2-dependent inhibition of the Na-K pump, of Na-K-2Cl cotransport, and of total and amiloride-sensitive 22Na uptake. Nifedipine failed to prevent hypoxia-induced transport inhibition in both cell types. In A549 cells, the inhibition of the Na-K pump and Na-K-2Cl cotransport occurred within approximately 30 min of hypoxia, was stable >20 h, and was reversed by 2 h of reoxygenation. There was also a reduction in cell membrane-associated Na-K-ATPase and a decrease in Na-K-2Cl cotransport flux after full activation with calyculin A, indicating a decreased transport capacity. [14C]serine incorporation into cell proteins was reduced in hypoxic A549 cells, but inhibition of protein synthesis with cycloheximide did not reduce ion transport. In AII and A549 cells, ATP levels decreased slightly, and ADP and the ATP-to-ADP ratio were unchanged after 4 h of hypoxia. In A549 cells, lactate, intracellular Na, and intracellular K were unchanged. These results indicate that hypoxia inhibits apical Na entry pathways and the basolateral Na-K pump in A549 cells and rat AII pneumocytes in culture, indicating a hypoxia-induced reduction of transepithelial Na transport and water reabsorption by alveolar epithelium. If similar changes occur in vivo, the impaired cation transport across alveolar epithelial cells might contribute to the formation of hypoxic pulmonary edema.

Relationship between plasma ammonia and blood lactate concentrations after maximal treadmill exercise in circumpubertal girls and boys

The purpose of the study was to define a relationship between plasma ammonia [NH3]pl and blood lactate concentrations [la-]b after exercise in children and to find out whether the [NH3]pl, determined during laboratory treadmill tests, may be useful as a predictor of the children's sprint running ability. A group of 20 girls and 14 boys trained in athletics or swimming and 8 untrained boys, aged 13.2 to 13.7 years, participated in the study. Their [NH3]pl and [la-]b were measured before and after incremental maximal treadmill exercise. In addition, the subjects' running performance was tested in 30-, 60- and 600- or 1000-m runs under field conditions. The [NH3]pl during the treadmill runs increased by 20.1 (SD 17.3), 24 (SD 16.7) and 10 (SD 4.3) mumol.l-1 in the girls, the trained boys and the untrained boys, respectively. The postexercise [NH3]pl correlated positively with [la-]b (r = 0.565 in the girls and 0.812 in the boys) and treadmill speed attained during the test (r = 0.489 in the girls and 0.490 in the boys). Significant correlations were also found between [NH3]pl obtained during the treadmill test and the times of 30- and 60-m runs (r = -0.676 and -0.648, respectively) in the boys but not in the girls. A comparison of the present data with those reported previously in adults showed that increases in [NH3]pl during maximal exercise in children would seem to be lower than in adult subjects both in absolute values and in relation to [la-]b.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine, glutamate, and ammonia exchanges in acutely ischemic swine myocardium

Coronary artery disease causes an increase in glutamate uptake and alanine output by the heart. We assessed the effects of acute myocardial ischemia on alanine and glutamate exchange and ammonia production in 10 anesthetized open-chest domestic swine (46.9 +/- 0.7 kg). Coronary blood flow was controlled through an extracorporal perfusion circuit. After a nonischemic control period (aerobic) the blood flow in the left anterior descending coronary artery was reduced by 60%. Arterial and anterior interventricular venous samples where drawn before and during 35 min of ischemia. Subendocardial blood flow, measured using radiolabeled microspheres, decreased from 1.27 +/- 0.16 to 0.25 +/- 0.09 (ml/g)/min, and left-ventricular wall-thickening fell to 47% of aerobic values. Ischemia resulted in a significant increase in the rate of glucose uptake (p less than 0.05) and a switch to net lactate production (p less than 0.01). Ischemia did not affect the rates of alanine output (-0.9 +/- 1.0 vs. -0.3 +/- 0.3 mumol/min) or glutamate uptake (-0.4 +/- 1.1 vs. 0.3 +/- 0.6 mumol/min), but did increase the venous-arterial difference for ammonia (-4.1 +/- 4.1 to 52.7 +/- 5.5 microM, p less than 0.0001) and the ammonia output (-0.33 +/- 0.24 to 1.34 +/- 0.14 mumol/min, p less than 0.0001). In conclusion, acute ischemia did not stimulate greater alanine output or glutamate uptake. However, acute ischemia did cause an increase in anaerobic glycolysis rate and ammonia output, which reflects a profound disruption in myocardial energy metabolism.

Blood ammonia and lactate concentrations during endurance exercise of differing intensities

The purpose of this study was to examine the changes of blood ammonia concentration ([NH3]b) during endurance exercise of differing intensities on the cycle ergometer and to compare [NH3]b to the changes observed in the simultaneously monitored blood lactate acid concentrations ([la-]b) measurements. A group of 16 endurance-trained athletes participated in the first part of the study and performed exercise of 30 min duration in a randomized order at intensities of 85%, 95%, 100% and 105% of their individual anaerobic threshold (Th(an,ind); E85-E105) which had been determined beforehand by a cycle exercise test with stepwise increments in intensity. In the second part, 18 average endurance-trained sports students underwent exhausting intensive endurance exercise (IEE) with an intensity of 95% of Th(an,ind). An extensive endurance exercise (EEE) of the same duration at 85% of the Th(an,ind) was carried out 2 days later. The [NH3]b increased constantly with increasingly duration of all exercise. However, [la-]b only increased during exercise with intensities above the Th(an,ind) (E105). The increase of [NH3]b was higher with higher exercise intensities. At IEE, [NH3]b was significantly higher from the 30th min than at EEE, whereas [la-]b increased from the 5th min. In conclusion, [la-]b responded more sensitively to the intensity of exercise than [NH3]b, but it is conceivable that in the future measurements of [NH3]b could be used to advise on the duration of endurance training. At present, however, the lack of experience and lack of appropriate values still hinders the systematic use of [NH3]b measurements in the physiological monitoring of sports training.